Hip implant with porous body

ABSTRACT

A hip implant has a neck body that connects to a bone fixation body. The bone fixation body has a porous structure with an elongated shape. An internal cavity is formed in the bone fixation body and includes a substance to stimulate bone growth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 11/409,611 filedon 24 Apr. 2006 now U.S. Pat. No. 8,506,642, which is a continuingapplication of Ser. No. 10/446,069 filed on May 27, 2003 now abandoned,both entitled “Hip Implant with Porous Body” and both being incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Much effort has been directed to integrating hip implants intosurrounding bone. Ideally, a hip implant would be placed into the femur,and thereafter bone would readily grow into the surface of the implant.To achieve this objective, many different surface technologies have beenapplied to hip implants. In some instances, the surface of the implantis roughened, grit-blasted, plasma-sprayed, or microtextured. In otherinstances, the surface is coated with a biological agent, such ashydroxylapatite (known as HA). In all of these instances, the goal isthe same: Produce a surface on the hip implant into which surroundingbone will grow or bond.

Porous coatings have also been applied to surfaces of hip implants.Porous surfaces are often thin coatings applied to the metallicsubstrate of the implant. Bone surrounding the implant can only growinto the thin coating itself. Bone cannot grow through the coating andinto the metallic substrate. The depth of bone growth into the implantis limited to the depth of the porous coating. Bone simply cannot growcompletely through the implant or deeply into the body of the implant.

SUMMARY OF THE INVENTION

One example embodiment is a hip implant that includes a bone fixationbody that connects to a neck body. The bone fixation body is formed of aporous structure that extends through a center of the bone fixation bodyin a cross-sectional view of the bone fixation body. An internal cavityis located in the porous structure of the bone fixation body. Thisinternal cavity includes a substance to stimulate bone growth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example embodiment of a hip implant.

FIG. 2 is a cross-sectional view of the implant of FIG. 1 embedded inthe intramedullary canal of a femur.

FIG. 3 is a side view of another example embodiment of a hip implant.

FIG. 4 is a cross-sectional view of FIG. 3 showing the hip implantembedded in the intramedullary canal of a femur.

FIG. 5 is a side cross-sectional view of yet another example embodimentof a hip implant.

FIG. 6 is a side view of yet another example embodiment a hip implant.

FIG. 7 is a top view of a horizontal cross section of an exampleembodiment.

FIG. 8 is a top view of a horizontal cross section of another exampleembodiment.

FIG. 9 is a top view of a horizontal cross section of yet anotherexample embodiment.

FIG. 10A is another example of a hip implant.

FIG. 10B is a cross-section taken along lines 10B-10B of the hip implantin FIG. 10A.

FIG. 11A is another example of a hip implant.

FIG. 11B is a cross-section taken along lines 11B-11B of the hip implantin FIG. 11A.

FIG. 12 is a cross-section of another example of a hip implant.

FIG. 13 is a cross-section of another example of a hip implant.

FIG. 14A is an example of a cross-section of a bone fixation body of ahip implant.

FIG. 14B is another example of a cross-section of a bone fixation bodyof a hip implant.

FIG. 14C is another example of a cross-section of a bone fixation bodyof a hip implant.

FIG. 14D is another example of a cross-section of a bone fixation bodyof a hip implant.

FIG. 14E is another example of a cross-section of a bone fixation bodyof a hip implant.

FIG. 15A is an example cross-section of a neck body of a hip implant.

FIG. 15B is an example cross-section of a bone fixation body of a hipimplant.

FIG. 16 is a partial cross-sectional view of a hip implant embedded in afemur of a patient.

DETAILED DESCRIPTION

In one example embodiment, a hip implant includes two separate anddistinct bodies, a neck body and a bone fixation body. Together, thesebodies connect together to form a femoral hip implant.

The bone fixation body is formed of a porous structure, such astitanium, tantalum, or other metals, polymers, or alloys suitable for ahip prosthesis. The bone fixation body has at least one cross-section inwhich the porous structure is completely porous. This completely porousstructure can extend through a portion of the bone fixation body (e.g.,throughout a cross-section) or through the entire body of the bonefixation body. For example in one embodiment, the bone fixation body iscompletely porous from its proximal to distal ends and does not includea metal substrate. In another example embodiment, a portion of the bonefixation body is completely porous and does not include a metalsubstrate. In at least one cross-sectional view then, the bone fixationbody has a porous structure with no solid metal substrate.

In one example embodiment, the porous structure extends entirely througha cross-section of the bone fixation body of the hip implant along theregion where the hip implant engages femoral bone. As such, the depth ofbone growth into the hip implant is not restricted to a thin porouscoating. Instead, bone can grow deeply into the bone fixation body ofthe hip implant or completely into and even through the bone fixationbody of the hip implant (i.e., bone can grow from one side of the hipimplant through its center and to another oppositely disposed side). Thehip implant can become fully integrated into surrounding bone with thestructure of bone dispersed throughout the bone fixation body of the hipimplant.

In one example embodiment, the geometric structure of the porousstructure of the bone fixation body is shaped and sized to emulate theshape and size of natural bone surrounding the hip implant. The porousstructure of the bone fixation body thus replicates the porous structureof natural bone itself. The porous structure readily accepts andencourages surrounding bone to grow into and even through the bonefixation body of the hip implant.

In one example embodiment, the bone fixation body includes an internalcavity with a substance that causes and/or stimulates bone growth. Thisinternal cavity can be enclosed within the bone fixation body without anegress or ingress. Alternatively, one or more openings in the bonefixation body or hip implant can lead to the internal cavity.

In one example embodiment, the bone fixation body and/or internal cavityinclude one or more substances to cause and/or stimulate bone growth.This substance can be placed throughout the bone fixation body and/orinternal cavity so bone grows deeply into the hip implant or completelythrough the hip implant from one side to an oppositely disposed side.Bone growth, as such, is not restricted to the surface of the hipimplant.

In one example embodiment, the substance in the internal cavity includesa porous structure that causes and/or stimulates bone growth from withinthe internal cavity. Bone grows from the internal cavity toward anexterior surface of the bone fixation body. After the hip implant isimplanted, bone can thus simultaneously grow from the internal cavitytoward an exterior surface of the bone fixation body and from theexterior surface of the bone fixation body toward the internal cavity.New bone growth thus concurrently occurs and originates from twoseparate and distinct locations (i.e., from locations within the hipimplant and from locations exterior to the hip implant).

As noted, the porous structure of the hip implant enables bone to growdeeply into or completely through the hip implant or portions of the hipimplant. Bone growth deep into the body of the hip implant provides astrong interface between the hip implant and surrounding natural bone.As such, the likelihood that the hip implant will loosen is reduced.Further, the overall long-term acceptance of the hip implant in the boneis increased. Further yet, the porous structure of the bone fixationbody and internal cavity reduce the overall weight of the hip implant.The size and shape of the internal cavity also enables the physicalproperties of the bone fixation body to more closely emulate thephysical properties of natural bone.

Referring to FIGS. 1 and 2, a hip implant 10 is shown according to anexemplary embodiment of the invention. Implant 10 is preferablyconstructed of a biocompatible material such as titanium, titaniumalloy, or other metals or alloys suitable for a hip prosthesis. Implant10 comprises two primary components or bodies, a neck body 14 and a bonefixation body 16.

The neck body 14 is located at the proximal end 18 of the hip implant 10and functions to connect the hip implant 10 to a spherically shapedfemoral ball 19 and acetabular component (not shown). The neck bodyextends from a flat or planar distal end surface 21 to a proximal endsurface 23. Further, the neck body has a base portion 20 that includes acollar 22 adapted to seat against a resected or end portion of a femur.An interface is adapted to connect the neck body to the femoral ball. Aneck portion 24 extends outwardly from the base portion 20. This neckportion has a short cylindrical configuration and has an end 26 with aslight taper. This end 26 is adapted to be received in a correspondinglyshaped and sized cylindrical recess 30 in the femoral ball 19. Together,end 26 and recess 30 form a Morse taper connection.

Preferably, the neck body 14 is formed of a biocompatible metal, such asa solid metal piece of titanium, titanium alloy or other metals oralloys suitable for a hip prosthesis. The body can be machined to have asize and shape shown in the figures or other sizes and shapes adaptedfor use as a hip implant.

The bone fixation body 16 has an elongated tapering shape that extendsfrom a flat or planar proximal end surface 40 to a rounded distal endsurface 42. The distal end surface 21 of neck body 14 connects or fusesto the proximal end surface 40 of the bone fixation body 16 at ajunction 44.

In the exemplary embodiments of FIGS. 1 and 2, bone fixation body 16 isformed from a porous metal, such as titanium. The body has a completelyporous structure that extends throughout the entire body from theproximal end surface 40 to distal end surface 42. Specifically, as shownin FIG. 2, body 16 does not include a solid metal substrate.

FIG. 2 shows the implant 10 embedded in a femur 50 of a patient. In thisembodiment, the implant is embedded into the intramedullary canal 52 ofthe femur. The length of the bone fixation body 16 extends along theregion where the implant contacts surrounding bone. As shown, the collar22 seats against a resected end 56 of the femur above an entrance 57 tothe intramedullary canal 59. In this embodiment, the bone fixation body16 extends into the intramedullary canal, and the neck body 14 extendsoutwardly from the resected end of the intramedullary canal and femur.Further, the proximal end surfaced 40 is adjacent the entrance 57 to theintramedullary canal.

As noted, the bone fixation body 16 has a porous structure that extendsthroughout the body from the proximal end surface to the distal endsurface. By “porous,” it is meant that the material at and under thesurface is permeated with interconnected interstitial pores thatcommunicate with the surface. The porous structure can be formed bysintering titanium, titanium alloy powder, metal beads, metal wire mesh,or other suitable materials, metals, or alloys known in the art.

The porous structure of body 16 is adapted for the ingrowth ofcancellous and cortical bone spicules. In the exemplary embodiment, thesize and shape of the porous structure emulates the size and shape ofthe porous structure of natural bone.

Preferably, the average pore diameter of body 16 is about 40 μm to about800 μm with a porosity from about 45% to 65%. Further, theinterconnections between pores can have a diameter larger than 50-60microns. In short, the geometric configuration of the porous structureshould encourage natural bone to migrate and grow into and throughoutthe entire body 16. Although specific ranges are given for porediameters, porosity, and interconnection diameters, these ranges areexemplary and are applicable to one exemplary embodiment. In otherembodiments, these ranges could be modified, and the resulting hipimplant still within the scope of the invention.

Preferably, body 16 is created with a sintering process. One skilled inthe art will appreciate that many variations exist for sintering, andsome of these variations may be used to fabricate the present invention.In the exemplary embodiment, the neck body is formed from a solid pieceof metal and prepared using conventional and known machining techniques.Next, a ceramic mold is provided. The mold has a first cavity that issized and shaped to match the size and shape of the bone fixation body.In this first cavity, the sintering material can be placed. The moldalso has a second cavity that is adjacent and connected to the firstcavity. This second cavity is sized and shaped to receive the neck body.The neck body is positioned in the second cavity such that the distalend surface is adjacent and continuous with the first cavity.

The sintering material is then placed into the first cavity. Thismaterial may be a titanium alloy powder, such as Ti-6Al-4V. Some of thispowder will contact the distal end surface of the neck body. The mold isthen heated to perform the sintering process. During this process, asthe material in the first cavity heats and sinters, the bone fixationbody forms and simultaneously bonds or fuses to the distal end surfaceof the neck body.

The size and shape of the pores and porous structure produced in thefirst cavity depend on many factors. These factors include, for example,the temperature obtained in the furnace, the sintering time, the sizeand shape of sintering material, the composition of the sinteringmaterial, and the type of ceramic mold used. These factors (and others)can be varied to produce a bone fixation body in accordance with thepresent invention. Further, these factors (and others) can be varied toproduce a strong bond between the bone fixation body and neck body.

Once the sintering process is finished, the neck body is directly fusedto the bone fixation body. These two bodies are now permanentlyconnected together to form the hip implant.

In the aforementioned sintering process, the bone fixation bodysimultaneously forms and attaches to the neck body. One skilled in theart though will appreciate that each of these bodies can be fabricatedindependently and subsequently connected together. If the bodies aremade separately, then they may be attached or fused together using knownwelding or brazing techniques, for example.

In FIG. 1, for example, the bone fixation body has an elongated taperingbody with a slight bow. The bone fixation body, though, may have otherconfigurations and still be within the scope of the invention. The sizeand shape of the body depend on the size and shape of the cavity of themold during the sintering process. This cavity can be shaped, forexample, to emulate the natural size, shape, and contour of a humanintramedullary canal. As such, the bone fixation body will morenaturally fit into the intramedullary canal and conform to the naturalanatomical contours of a human patient.

FIGS. 3 and 4 show another hip implant 50 according to an exemplaryembodiment of the invention. With some differences, implant 50 issimilarly configured to the implant 10. As one difference, the neck body60 of implant 50 has two different and distinct regions on its outersurface. A first region 62 has a smooth outer surface. A second region64 has a bone-engaging surface that is contiguous and adjacent to thefirst region 62 on one side and contiguous and adjacent the porous bonefixation body 66 on the other side. The second region is non-porous andis shaped as a band that extends completely around the neck body. Thissecond region can be formed on the outer surface of the neck body withvarious techniques. These techniques include, for example, coating withHA, grit-blasting, etching, micro-texturing, other non-porous surfacetreatments, or combinations of these techniques. This surface 64 isprovided as an intermediate zone between the porous body and the smoothfirst region 62.

As shown in FIG. 4, the second region 64 is below collar 68 and ispositioned into the intramedullary canal to contact bone. Region 64,then, contacts bone, and region 62 does not contact bone and extendsabove it.

FIG. 5 shows another implant 70 according to another exemplaryembodiment of the invention. With some differences, implant 70 issimilarly configured to the implant 10. As one difference, neck body 72includes a male protrusion 74 that extends outward from base portion 76.This protrusion 74 is adapted to extend partially into the bone fixationbody 78 of implant 70. The protrusion 74 forms a core for the bonefixation body. As shown in FIG. 5, this protrusion extends past theproximal end surface 80 and into the bone fixation body. The depth ofthe protrusion into the bone fixation body can be increased or decreasedin various embodiments and still remain within the scope of theinvention. For example, the protrusion can partially extend into thebone fixation body and remain substantially near the proximal endsurface. Alternatively, the protrusion can extend farther into the bonefixation body toward the distal end surface 82. In this latterembodiment, the protrusion gradually tapers as it extends toward thedistal end surface.

The size and shape of the protrusion can also have various embodimentsand still remain within the scope of the invention. For example, theprotrusion can be cylindrical or polygonal, such as rectangular orsquare. Other configurations are possible as well; the protrusion cantaper or have longitudinal ribs placed along its outer surface. The sizeand shape of the protrusion can have various embodiments to servevarious functions. For example, the protrusion can be sized and shapedto provide a strong connection between the neck body and bone fixationbody. The protrusion can be sized and shaped to provide ananti-rotational interface between the neck body and bone fixation body.Further, the protrusion can be sized and shaped to provide additionalstrength to the bone fixation body or more equally or efficientlydistribute loads from the neck body to the bone fixation body. Otherfactors as well may contribute to the design of the protrusion.

FIG. 6 shows another implant 90 according to an exemplary embodiment ofthe invention. Implant 90 has a bone fixation body 92 with an outersurface that has a plurality of undulations 94, such as hills andvalleys. These undulations may be provided as tiny ripples or waves.Alternatively, the undulations may be larger and more rolling.Regardless, the undulations are adapted to firmly secure the implantinto the intramedullary canal of the femur after the implant is placedtherein.

As shown in FIG. 6, the undulations extend along the entire length ofthe bone fixation body 92 from the proximal end surface 96 to the distalend surface 98. In alternative embodiments, the undulations do notextend along the entire length of the bone fixation body, but partiallyextend along this body.

FIGS. 7-9 show various longitudinal cross-sectional shapes of the bonefixation body for different exemplary embodiments of the invention. Thebone fixation body may have one single longitudinal cross-sectionalshape, or the body may have numerous different longitudinalcross-sectional shapes. FIGS. 7-9 represent examples of some of theseshapes.

FIG. 7 shows a trapezoidal longitudinal cross-sectional shape. FIG. 8shows a triangular longitudinal cross-sectional shape. FIG. 9 shows anelliptical or oval longitudinal cross-sectional shape.

The bone fixation body can be adapted to induce bone growth partiallyinto or entirely through the body. The body, for example, can be dopedwith biologically active substances. These substances may containpharmaceutical agents to stimulate bone growth all at once or in atimed-release manner. Such biological active substances are known in theart.

FIGS. 10A and 10B show a hip implant 100 according to an exampleembodiment. The hip implant 100 comprises two primary components orbodies, a neck body 114 and a bone fixation body 116.

The neck body 114 is located at the proximal end 118 of the hip implant100 and functions to connect the hip implant 100 to a spherically shapedfemoral ball and acetabular component. The neck body extends from one ormore flat or planar distal end surfaces 121 to a proximal end surface123. A neck portion 124 extends outwardly from a base portion 120. Thisneck portion has a short cylindrical configuration and has an end 126with a slight taper. This end 126 is adapted to be received in acorrespondingly shaped and sized cylindrical recess in the femoral ball(shown in FIGS. 1 and 2).

Preferably, the neck body 114 is formed of a biocompatible metal, suchas one or more of a solid metal piece of titanium, titanium alloy,polymer, or other metals or alloys suitable for a hip prosthesis. Theneck body can be machined, casted, molded, or otherwise configured tohave a size and shape shown in the figures or other sizes and shapesadapted for use as a hip implant.

The bone fixation body 116 has an elongated tapering shape that extendsfrom a proximal end 140 to a rounded distal end 142. The proximal endincludes one or more flat or planar surfaces 144. One or more of thesesurfaces connect to the distal end surfaces 121 of the neck body 114 atan interface or junction 146.

As shown in FIG. 10B, the bone fixation body 116 forms a shell 148 witha completely porous structure that extends throughout the entire bonefixation body from the proximal end 140 to the distal end 142. Thisshell 148 has a hollow center that forms an internal chamber or cavity150 located inside the bone fixation body 116. The internal cavity 150extends from a location adjacent the interface 146 to the distal end142. A circular opening 152 leads into the internal cavity 150 and formsat the distal end 142 of the bone fixation body 116. The internal cavity150 is thus enclosed inside of the porous structure of the bone fixationbody 116.

As shown in FIG. 10B, the internal cavity 150 includes a substance 154to cause or stimulate bone growth. This substance 154 fills the internalcavity 150 from a proximal end surface of the internal cavity to anoppositely disposed distal end surface of the internal cavity.Alternatively, the substance can partially fill the internal cavity orbe absent from the internal cavity.

A shape and/or size of the internal cavity 150 can vary along itslongitudinal length. In an example embodiment, this shape matches oremulates the external shape of the bone fixation body 116. As the sizeand/or shape of the bone fixation body 116 changes, the size and/orshape of the internal cavity 150 correspondingly changes. With regard tosize for example, as the cross-sectional diameter of the bone fixationbody increases or decreases, the cross-sectional diameter of theinternal cavity proportionally increases or decreases to match theincreases or decreases in the diameter of the bone fixation body. Withregard to shape for example, the bone fixation body 116 has an elongatedcylindrical or elliptical shape at a distal end portion 156 incross-section. Likewise, the internal cavity 150 has an elongatedcylindrical or elliptical shape at this distal end portion 156. At aproximal end portion 158, the bone fixation body has a rectangular ortrapezoidal shape in cross-section. Likewise, the internal cavity 150has a rectangular or trapezoidal shape at this proximal end portion 158.Thus, as the size and/or shape of the bone fixation body changes alongits longitudinal length, the size and/or shape of the internal cavitycan also change to match with or correspond to these changes.

In an example embodiment, the internal cavity 150 is centrally locatedinside of the bone fixation body 116 such that the sides or walls 160 ofthe internal cavity are equally spaced from an external surface 162 ofthe bone fixation body. The walls 160 can include one or more grooves164 formed in the porous structure of the bone fixation body. Thesegrooves form one or more channels that extend from the circular opening152 to an end surface 166 of the internal cavity 150.

As shown in FIG. 10B, the internal cavity 150 has a larger diameter incross-section adjacent the interface 146 at the proximal end 158 than atthe distal end 156. The size of the internal cavity narrows and tapersas it transitions from the proximal end of the hip implant toward thedistal end of the hip implant.

While the hip implant 100 is being positioned into the femur of thepatient, bone, tissue, and/or blood enters and fills the internal cavity150. As the hip implant passes into the medullary canal of the femur,bone, tissue, and/or blood are forced into the internal cavity andtravel upwardly along the grooves 164 toward the end surface 166. Thegrooves guide and facilitate the passage of bone, tissue, and/or bloodinto the internal cavity. For example, bone travels in the grooves 164from the opening 152 to the end surface 166 in order to fill or collectwithin the internal cavity 150.

The grooves 164 can be straight and extend parallel to each other fromthe opening 152 to the end surface 166. Alternatively, the grooves canbe nonlinear, such as being curved or spiraling. Grooves facilitate thetransfer of bone, tissue, and/or blood into the internal cavity 150while the hip implant 100 is being forced, pressed, or inserted into thefemur. Alternatively, the internal cavity 150 can be formed withoutgrooves.

FIGS. 11A and 11B show a hip implant 200 with a neck body 202 thatconnects to a bone fixation body 206 according to an example embodiment.With some differences, the hip implant 200 is similarly configured tothe hip implant 100 in FIGS. 10A and 10B. As one difference, the hipimplant 200 includes an internal cavity 210 that is enclosed and trappedwithin the bone fixation body 206. One of end this internal cavity 210is located near or adjacent a junction 218 where the neck body 202connects to a proximal end 214 of the bone fixation body 206. Anotherend of this internal cavity 210 extends toward a distal end 216 of thebone fixation body 206.

In an example embodiment, the internal cavity 210 is completely enclosedwithin the bone fixation body 206. The bone fixation body 206 completelysurrounds the sides, the top, and the bottom of the internal cavity 210(i.e., the internal cavity is surrounded on all sides by the porousstructure). As such, the internal cavity 210 lacks an ingress (such as ahole or a passageway) for entering the cavity or an egress for exitingthe cavity (such as a hole or a passageway). Nonetheless, theopen-celled configuration of the porous structure of the bone fixationbody does allow bone to grow into and through the bone fixation body.Thus, the internal cavity can still communicate with the porousstructure of the bone fixation body and with bone external to the bonefixation body through the interconnected interstitial pores to enablebone growth since the internal cavity is surrounded by and formed withinan open-celled porous structure. Alternatively, the bone fixation body206 includes openings, holes, and/or passageways from an externalsurface 238 to the internal cavity 210.

As shown in FIG. 11B, the internal cavity 210 includes a substance 220to cause or stimulate bone growth. This substance 220 fills the internalcavity 210 from a proximal end surface 230 of the internal cavity to anoppositely disposed distal end surface 232 of the internal cavity.Alternatively, the substance can partially fill the internal cavity orbe absent from the internal cavity.

In one example embodiment, the substance 220 is trapped within theenclosed internal cavity. For example, the substance is placed in theinternal cavity during manufacturing or formation of the hip implant.Alternatively, the substance is placed in the internal cavity after thehip implant is constructed. For instance, a small opening is formedthrough the hip implant, the substance is placed through the opening andinto the internal cavity, and then the opening is sealed and/or closed.As yet another example, the substance is liquefied and forced throughthe interconnected interstitial pores of the bone fixation body and intothe internal cavity. In this example, the substance travels from theexterior surface 238, through the bone fixation body 206, and into theinternal cavity 210.

In an example embodiment, the substance in the internal cavity and/orporous structure of the bone fixation body activates and/or grows bonewhen bone, tissue, and/or blood enter into the internal cavity. Forexample, one or more blood vessels, arteries, and canals supply blood tothe substance.

FIG. 12 shows a cross-sectional view of another hip implant 300according to an example embodiment. The hip implant 300 includes a neckbody 302, a bone fixation body 304, and a distal body 306. The neck body302 connects to the bone fixation body 304 at a junction 310, and thebone fixation body 304 connects to the distal body 306 at a junction312.

The bone fixation body 304 includes a porous structure 320 thatsurrounds an internal cavity 322. This internal cavity extends from alocation adjacent the junction 310 to an opening 326 at the distal endof the distal body 306. A substance 330 to cause and/or stimulate bonegrowth is located inside of the internal cavity of the bone fixationbody and the distal body.

Internal cavity 322 extends through a center of the distal body 306along a longitudinal central axis of the distal body. Bone, tissue,and/or blood travel through the opening 326, through the internal cavityof the distal body 306, and into the internal cavity at the proximal endof the bone fixation body 304. For example, bone, tissue, and/or bloodenter the internal cavity of the bone fixation body and distal bodywhile the hip implant is being implanted into the femur of the patient.

In an example embodiment, the internal cavity of the bone fixation bodyand distal body are in fluid communication with each other such that thesubstance 330 or another substance (such as bone, tissue, and/or blood)located inside these cavities can flow or migrate between the bonefixation body and the distal body. As discussed herein, the substance,however, is not limited to being a fluid, but can be a solid structure,such as a scaffold, a membrane, a powder, a metal, a polymer, and/orother biocompatible materials.

FIG. 13 shows a cross-sectional view of another hip implant 400according to an example embodiment. The hip implant 400 includes a neckbody 402, a bone fixation body 404, and a distal body 406. The neck body402 connects to the bone fixation body 404 at a junction 410, and thebone fixation body 404 connects to the distal body 406 at a junction412.

The bone fixation body 404 includes a porous structure 420 thatsurrounds an internal cavity 422. This internal cavity extends from alocation adjacent the junction 410 to a location adjacent the junction412. A substance 430 to cause and/or stimulate bone growth is locatedinside of the internal cavity 422 of the bone fixation body 404.

In FIGS. 12 and 13, the neck body thus forms a proximal section of thehip implant; the bone fixation body forms a middle section of the hipimplant; and the distal body forms a distal section of the hip implant.Additionally, the bone fixation body is formed of a porous structure,while the neck body and the distal body include a non-porous structure,such as having a substrate or base formed of solid metal, metal alloy,polymer, and/or other biocompatible material. For example, the neck bodyand distal body are formed of solid metal with a porous structure,microtexture, or bone stimulating substance on their outer surfaces. Thenon-porous structure of the neck body and the distal body can be thesame, similar, or different from each other. As one example, the neckbody and the distal body include a non-porous substrate formed of solidmetal, while the bone fixation body is formed of a porous substrate. Asanother example, the neck body is formed having a first material (suchas a solid substrate or underlying layer formed of one metal); the bonefixation body is formed having a second material different than thefirst material (such as a porous structure); and the distal body isformed having a third material different than the first and secondmaterials (such as solid substrate or underlying layer formed of anothermetal or a porous structure formed to include a different material thanthe porous structure of the bone fixation body).

In FIG. 13, the neck body 402 and the distal body 406 are structurallystronger than the bone fixation body 404 since they include a non-porousstructure whereas the bone fixation body is formed to have a porousstructure. As such, the bone fixation body is configured so that bonecan grow completely through the porous structure. By contrast, the neckbody and the distal body are configured so that bone can grow into anouter surface but not into and through center of the bodies since theselocations have cores or centers filled with solid metal. For example,the outer surfaces of the neck and distal bodies are micro-textured orcovered with a porous structure. These surfaces can integrate withsurrounding bone after the hip implant is implanted in the femur.

FIGS. 10B, 11B, 12, and 13 show the hip implant with an internal cavity.The size and shape of this internal cavity can vary depending on, forexample, the size and shape of the hip implant, the substance includedin the internal cavity, the mechanical properties desired for theimplant, and the material used to fabricate the porous structure. By wayof example, these shapes of the internal cavity include, but are notlimited to, cylinders (such as right circular cylinders having across-section as a circle, elliptic cylinders having a cross-section asan ellipse, hyperbolic cylinders having a cross-section as a hyperbola,parabolic cylinders having a cross-section as a parabola, obliquecylinders having top and bottom surfaces displaced from each other, andtapered cylinders), cones (such as right cones, oblique cones, truncatedcones, and elliptical cones), wheels (such as a shape having acylindrical core with passageways extending off from this core),spheres, cuboids, polyhedrons, polytopes, pyramids, linear andnon-linear tunnels and pathways, symmetric and asymmetric voids andcavities, three dimensional shapes (such as shapes having curved lines,straight lines, closed configurations, and/or open configurations), andcombinations of these shapes.

Additionally, the size and shape of the internal cavity can be adjustedto provide a closer biomechanical match of strength, stiffness, andarchitectural structure between the hip implant and the surroundingbone. The combination of pores in the porous structure and space of theinternal cavity reduces the overall stiffness values of the hip implantso it can more closely resemble the stiffness values and properties ofnatural bone.

FIGS. 14A-14E show example horizontal cross-sections of hip implantswith differently shaped internal cavities. These cross-sections showexamples of hip implants in accordance with example embodiments.

FIG. 14A is an example of a cross-section of a hip implant 500A having abone fixation body 510A with an internal cavity 520A that is filled witha substance 530A to cause and/or stimulate bone growth. The bonefixation body 510A and the internal cavity 520A have a circular shape.An outer wall 540A that forms the exterior circumferential wall of theinternal cavity is equally spaced from an outer wall 550A that forms theexterior circumferential wall of the bone fixation body.

FIG. 14B is an example of a cross-section of a hip implant 500B having abone fixation body 510B with an internal cavity 520B that is filled witha substance 530B to cause and/or stimulate bone growth. The bonefixation body 510B and the internal cavity 520B have an ellipticalshape. An outer wall 540B that forms the exterior circumferential wallof the internal cavity is equally spaced from an outer wall 550B thatforms the exterior circumferential wall of the bone fixation body.

FIG. 14C is an example of a cross-section of a hip implant 500C having abone fixation body 510C with an internal cavity 520C that is filled witha substance 530C to cause and/or stimulate bone growth. The bonefixation body 510C and the internal cavity 520C have a rectangular shapewith rounded ends. An outer wall 540C that forms the exteriorcircumferential wall of the internal cavity is equally spaced from anouter wall 550C that forms the exterior circumferential wall of the bonefixation body.

FIG. 14D is an example of a cross-section of a hip implant 500D having abone fixation body 510D with an internal cavity 520D that is filled witha substance 530D to cause and/or stimulate bone growth. The bonefixation body 510D and the internal cavity 520D have a trapezoidalshape. An outer wall 540D that forms the exterior circumferential wallof the internal cavity is equally spaced from an outer wall 550D thatforms the exterior circumferential wall of the bone fixation body.

FIGS. 14A-14D show that the shape of the internal cavity and the shapeof the corresponding bone fixation body are similar. These shapes,however, can be different such as shown in FIG. 14E.

FIG. 14E is an example of a cross-section of a hip implant 500E having abone fixation body 510E with an internal cavity 520E that is filled witha substance 530E to cause and/or stimulate bone growth. The bonefixation body 510E has a trapezoidal shape, and the internal cavity 520Ehas an elliptical shape. A distance varies between the outer wall 540Ethat forms the exterior circumferential wall of the internal cavity andan outer wall 550E that forms the exterior circumferential wall of thebone fixation body.

A size of the internal cavity with respect to the hip implant can vary.This size can change by adjusting the volume that the internal cavityoccupies within the bone fixation body. By way of example, FIG. 14Ashows that the bone fixation body 510A has circular shape with a radiusR1, while the internal cavity has a circular shape with a radius R2. Anarea occupied by the bone fixation body is: A1=π(R1)²−π(R2)², and anarea occupied by the internal cavity is: A2=π(R2)². A percentage of areaoccupied by the internal cavity with respect to the bone fixation bodyin a cross-sectional view is: PA=(A2/A1)×100. This percentage of areaoccupied by the internal cavity (PA) can have values that range fromabout 10%-90% (such as having example values of about 10%, 15%, 20%,25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 79%, 75%, 80%, 85%, or90%). As another example, this percentage of area occupied by theinternal cavity (PA) has a range of about 30%-70%.

FIGS. 1-6, 10A, 10B, 11B, 11B, 12, and 13 show that the porous structureof the bone fixation body connects to the neck body at an interface or ajunction. The particular cross-sectional shape of this junction wherethe two bodies connect depends on the shape of the bone fixation andneck bodies. For example, if the bone fixation body and the neck bodyare both formed as right cylinders at the junction of their interface,the junction (when viewed in a cross-section) is circular. Such ajunction includes the entire volume of this circular cross-section sincethe circular cross-section of the bone fixation body abuts the circularcross-section of the neck body. This abutment of two circularcross-sections (or other shaped cross-sections) provides strength to theimplant at the junction where the non-porous structure of the neck bodyconnects to the porous structure of the bone fixation body.

By way of example, FIGS. 15A and 15B show cross-sections of an examplejunction. FIG. 15A is an example of a hip implant 600 showing across-section of its neck body 610 at the junction where the bonefixation body connects to the neck body. The neck body 610 has atrapezoidal shape and is formed to have a non-porous substrate, such asbeing formed of solid metal. FIG. 15B is an example of the hip implant600 showing a cross-section of its bone fixation body 620 at thejunction. The bone fixation body 620 has a trapezoidal shape and isformed to have a porous structure as the substrate. A size and shape ofthe bone fixation body match a size and shape of the neck body at thejunction.

Example embodiments include a bone fixation body with a porous structurethat connects to a neck body with a non-porous structure. The structureof the neck body can be stronger than the structure of the bone fixationbody. For example, the neck body is formed of a non-porous structure toprovide strength to the hip implant and structural support for theporous structured bone fixation body. This added strength is usefulsince forces transfer to the hip implant at the neck body.Alternatively, the neck body can be formed of a porous structure, butthis porous structure should be strong enough to endure the forcesencountered at the proximal end of the hip implant.

FIG. 16 is a partial cross-sectional view of a hip implant embedded in afemur of a patient. For example, this cross-section can represent theproximal end of the bone fixation body of the hip implant shown in FIGS.10B, 11B, 12, and 13.

As shown in FIG. 16, the hip implant 700 includes a bone fixation body710 that is embedded in a femur bone 720 of a patient. This boneincludes cortical bone and/or cancellous bone. The bone fixation body710 includes an internal cavity 730 that is filled with a substance 740to cause and/or stimulate bone growth.

Once the hip implant 700 is implanted into the femur bone 720, bonesimultaneously begins to grow with natural bone growing inwardly towardthe internal cavity 730 and bone from the substance growing outwardlyfrom the internal cavity 730 toward the natural bone 720 that is growinginwardly. Natural bone 720 surrounding the hip implant 700 begins togrow into the outer surface 750 of the bone fixation body 710. At thesame time, bone begins to grow outwardly from the internal cavity 730and toward the outer surface 750. The substance causes and/or stimulatesbone to grow outwardly from the internal cavity.

The porous structure of the bone fixation body thus supports bone growthinwardly towards the center of the hip implant and outwardly away fromthe center of the hip implant. Thus, bone grows from two different andseparately located sources (one source being the natural bone locatedoutside of the hip implant and a second source being the substance 740located inside of the hip implant). This process of concurrently growingbone from two different locations (i.e., from within the hip implant andfrom outside of the hip implant) decreases the time required for bone togrow throughout the hip implant including the center of the hip implantwhere the substance is located. For example, the time required for boneto grow from one side of the bone fixation body to an oppositelydisposed side of the bone fixation body is reduced since bone isconcurrently growing both toward the center of the bone fixation bodyand outwardly from this center immediately after the hip implant isimplanted into the femur. This process also decreases the time requiredfor bone to completely fill the porous structure of the bone fixationbody since bone grows in multiple different directions. For instance,bone simultaneously grows in directions from the internal cavity throughsides of the cavity, through the top of the cavity, and through thebottom of the cavity. Additionally, bone grows through the sides and thebottom of the exterior surfaces of the bone fixation body. The hipimplant is thus able to more quickly fully integrate with bone afterbeing implanted (for example, more quickly have bone grow throughout theentire structure of the bone fixation body). Growing bone from thecenter of the hip implant thus expedites the time required to completethe bone integration process.

In an example embodiment, the porous structure of the bone fixation bodyis different than the structure of the substance located in the internalcavity in the bone fixation body. The geometry and material compositionof the porous structure of the bone fixation body and the substance inthe internal cavity both induce bone formation throughout the internalcavity and the bone fixation body. The geometry and material compositionof the porous structure of the bone fixation body, however, alsoprovides strength to the hip implant since it bears loads from forces onthe hip implant (for example, forces generated while the patient isstanding and/or moving). A majority of these loads pass along the bonefixation body and not to the substance located in the internal cavity.As such, the geometry and material composition of the substance can befor stimulating bone growth, whereas the geometry and materialcomposition of the bone fixation body can be for stimulating bone growthand for providing strength to the hip implant.

In an example embodiment, the substance includes a porous structuredscaffold that is inserted or fabricated in the internal cavity of thebone fixation body. This scaffold has a geometry and materialcomposition to induce bone growth through the internal cavity and intothe surrounding walls of the bone fixation body. In one exampleembodiment, this scaffold would not have to support equivalent loadssupported by the exterior of the bone fixation body surrounding theinternal cavity. Alternatively, the geometry and material composition ofthe substance located in the internal cavity can also be for supportingloads and providing strength to the hip implant.

In an example embodiment, the substance in the internal cavity isactivated when the hip implant is placed into the femur of the patient.As one example, looking to FIGS. 10B and 12, the substance is located inthe internal cavity. While the hip implant is being placed into thefemur, bone, tissue, blood, and other substances pass through theopening at the distal end, come in contact with the substance in theinternal cavity, and activate this substance to begin stimulating bonegrowth in the internal cavity. As another example, looking to FIGS. 11Band 13, while the hip implant is being placed into the femur, a fluid(including one or more of bone, tissue, blood, and other substancescreated from the implantation procedure) seeps or passes through theporous structure of the bone fixation body and comes in contact with thesubstance in the internal cavity. This fluid activates this substance tobegin stimulating bone growth in the internal cavity. Alternatively,bone growth and bone stimulation properties of the substance areactivated with an agent (for example, an external agent applied to thestructure and/or the substance during implantation). As yet anotherexample, passageways or holes are placed in the bone fixation body.These passageways allow bone, tissue, blood, and other substances toenter the internal cavity and cause, assist, and/or activate bonegrowth. As another example, the substance in the internal cavityactivates after the hip implant is implanted and blood is supplied tothe substance.

The substance to cause or stimulate bone growth can be formed from avariety of different materials and different processes. As one example,the substance includes a mixture of one or more bone morphogeneticproteins (BMPs) and one or more carriers. For instance, this mixtureincludes BMP 4, collagen, and a polymer, such as poly(lactic-co-glycolicacid) (PLGA) or poly(L-lactide) (PLLA). As another example, thesubstance includes one or more of natural bone and/or tissue and/orblood from the patient receiving the implant, tantalum, an acrylatebased polymer, biphasic calcium phosphate (BCP), carboxymethylcellulose(CMC), hydroxypropylmethylcellulose (HPMC), hydroxyapatite (HA),tricalcium phosphate (TCP), stem cells (including human embryonic stemcells and adult stem cells), bone marrow-derived stromal cells, humanbone-derived cells (hPBDs), biodegradable polymers (such aspoly(glycolic acid) (PGA) and poly(lactic acid) (PLA)), poly(α-hydroxyacids), calcium-phosphates (CaP) (such as β-tricalcium phosphate (β-TCP)and α-tricalcium phosphate (α-TCP)), poly(D,L-lactide) (PDLLA),injectable bone (for example, injectable bone that includes calciumphosphate and/or calcium sulphate), allotransplantation (i.e., boneand/or tissue from a same species, such as allografts and autografts),xenotransplantation (i.e., bone and/or tissue from another species),rattan wood, bioactive glasses (such as a bioactive glass foamscaffold), cancellous structured titanium, resorbable porous structures,class A and class B bioactive materials, bone grafts, and othermaterials that cause and/or stimulate bone growth.

Furthermore, the substance can be formed with various geometricconfigurations, such as including one or more of a liquid, a powder,and/or a solid. These configurations include both porous structures andnon-porous structures. Further yet, these configurations include thesubstance being formed to have a three-dimensional solid structure, suchas a scaffold or scaffolding, a porous structure, a structure thatimitates cancellous bone, a structure that imitates cortical bone, amesh, and/or a solid platform that provides a framework for the supportand growth of bone. By way of example, the substance is formed into athree-dimensional porous scaffold and placed in the internal cavity (forexample, PGA, PLA, and/or PLGA scaffolds). The pore size and porosity ofthe scaffold can be optimized to induce colonization and proliferationof cells. For example, the pore sizes range from about 150 μm-700 μm),and the porosity of the scaffold ranges from about fifty percent (50%)to ninety percent (90%).

As discussed herein, the porous structure of the substance and/or thebone fixation body can be formed from a variety of different materialsand different processes. As one example, the porous structure is formedfrom one or more of polymers, ceramics, and biocompatible metals andmetal alloys. For example, the porous structure is constructed withtantalum, titanium, a titanium (Ti) alloy, such as titanium with one ormore of zirconium (Zr), niobium (Nb), tin (Sn), silicon (Si), molybdenum(Mo), and tantalum (Ta)), biocompatible polymer, and/or a biocompatiblemetal or metal alloy.

By way of example, the porous structure is formed from one of a castingprocess and/or a powder metallurgy process. The casting process caninclude one or more of vacuum melting and annealing, hot rolling, scaleremoval, machining, and surface preparation. The powder metallurgyprocess can include one or more of a pre-alloying process (such asfabricating alloyed powder using gas atomization and melting) and ablending of metals to obtain a predetermined alloy composition. Metalpowder is then cold pressed into a shaped and sintered. The porousstructure can also be fabricated using one or more of sintering,casting, plasma-spraying, sputter deposition techniques, and metallicdeposition techniques.

As another example, the porous structure is formed by coating a solidskeleton or a hollow skeleton with one or more of a polymer, a metal,and/or a metal alloy. For example, a carbon skeleton is coated withtantalum using a vapor deposition process. For instance, tantalum isdeposited on a vitreous carbon foam structure.

As yet another example, the porous structure is formed from a metalinjection molding (MIM) process. For example, metals and/or polymers aremixed to form a feedstock that is then shaped. The polymer is thenremoved, and the structure is heated, machined, and coated.

Furthermore, the porous structure can include opens cells (i.e., poresconnected to each other through channels, voids, interstices, etc.),closed cells (i.e., pores disconnected from each other), andcombinations of open and closed cells.

Additionally, the porosity of the porous structure can be constantthroughout the porous structure or change within the porous structure.For instance, the porous structure can have a gradient porosity in whichthe porosity changes from the surface of the bone fixation body to thecenter of the bone fixation body (for example, the porosity near thesurface of the bone fixation body is different than the porosity insidethe internal cavity).

The porosity can also increase or decrease at different locations alongthe hip implant. For instance, the porosity of the porous structurewhere the bone fixation body contacts cortical bone can be differentthan the porosity where the bone fixation body contacts cancellous bone.The porosity of the porous structure where the hip implant contactscortical bone can be lower than the porosity of the porous structurewhere the hip implant contacts cancellous bone. Looking to FIG. 10B forexample, the bone fixation body 116 at or adjacent the proximal end 140where the hip implant 100 contacts cortical bone has a differentporosity than where the bone fixation body 116 contacts cancellous boneat or adjacent the distal end 142. Thus, the bone fixation body can havea first porosity at the proximal end and a second, different porosity atother locations, such as near or at the distal end.

Although illustrative embodiments have been shown and described, a widerange of modifications, changes, and substitutions is contemplated inthe foregoing disclosure; and some features of the embodiments may beemployed without a corresponding use of other features. Accordingly, itis appropriate that the appended claims be construed broadly and in amanner consistent with the scope of the embodiments disclosed herein.

What is claimed is:
 1. A method, comprising: machining a neck bodyformed of solid metal to include a neck that receives a femoral ball andhaving a male protrusion that extends outwardly from the neck body;fabricating, separately from the neck body, a bone fixation body with aporous metal structure that extends completely throughout the bonefixation body with the porous metal structure having a size and a shapethat emulate a size and a shape of a porous structure of natural humanbone; and attaching, after the bone fixation body is separatelyfabricated from the neck body, the bone fixation body to the neck bodyto create a hip implant such that the male protrusion extends into andpermanently attaches with the porous metal structure of the bonefixation body to create the hip implant before the hip implant isimplanted, wherein the porous metal structure of the bone fixation bodyincludes a trapezoidal shape in a horizontal cross-sectional view of thehip implant, and the male protrusion extends to a distal end of the hipimplant.
 2. The method of claim 1, wherein the bone fixation body andthe neck body have an area with a polygonal shape in a horizontalcross-sectional view of the hip implant.
 3. The method of claim 1,wherein the male protrusion of the neck body has a noncircular taperingshape and extends into the porous metal structure of the bone fixationbody such that the porous metal structure surrounds an exterior surfaceof the male protrusion.
 4. The method of claim 1, wherein the neck bodyengages the bone fixation body at an interface that has a trapezoidalshape in a horizontal cross-sectional view.
 5. The method of claim 1,wherein the bone fixation body has an elongated tapering body with abow.
 6. The method of claim 1, wherein the bone fixation body is bondedto the neck body after being separately fabricated from the neck bodyand includes an agent to stimulate bone growth through a center of thebone fixation body in a horizontal cross-sectional view of the hipimplant.
 7. The method of claim 1, wherein the male protrusion of theneck body has one of a square shape and a rectangular shape and taperswhile extending toward the distal end of the hip implant.
 8. A method,comprising: machining solid metal to form a neck body that includes aneck to receive a femoral ball and that includes a male protrusion thatextends outwardly from the neck body; making, separately from the neckbody, a bone fixation body with a porous metal structure that extendsthroughout the bone fixation body with interconnected pores having ageometric structure with a shape and a size that emulate a shape and asize of natural human bone; and connecting, after the bone fixation bodyis separately made from the neck body, the bone fixation body to theneck body to create a hip implant such that the male protrusion extendsinto the bone fixation body in order to permanently connect the neckbody to the bone fixation body and create the hip implant, wherein theporous metal structure of the bone fixation body includes a trapezoidalshape in a horizontal cross-sectional view of the hip implant, and themale protrusion extends toward a distal end of the hip implant.
 9. Themethod of claim 8, wherein the bone fixation body is fused to the neckbody after the bone fixation body is made separately from the neck body.10. The method of claim 8, wherein the male protrusion of the neck bodyis a core for the bone fixation body and has a polygonal and taperingshape that extends into the porous metal structure of the bone fixationbody.
 11. The method of claim 8, wherein the bone fixation body tapersand includes a bow shape.
 12. The method of claim 8, wherein the bonefixation body includes a location with a polygonal shape in a horizontalcross-sectional view of the hip implant, and the porous metal structurefills a center of the polygonal shape in the horizontal cross-sectionalview of the polygonal shape.
 13. The method of claim 8, wherein theporous metal structure is uniform.
 14. A method, comprising: forming aneck body having a proximal end that connects with an acetabularcomponent, having a distal end surface with a protrusion that extendsoutwardly therefrom, and being formed of solid metal; forming a bonefixation body having an elongated tapering shape and having a porousmetal structure with a size and a shape that emulate a size and a shapeof a porous structure of natural human bone; and engaging, after theneck body and the bone fixation body are separately formed, the bonefixation body to the neck body such that the porous metal structurepermanently engages to the protrusion and the protrusion extends to adistal end of a hip implant and tapers and extends into an opening ofthe bone fixation body such that the porous metal structure surroundsand engages an exterior surface of the protrusion that extends into thebone fixation body, wherein the bone fixation body includes atrapezoidal shape in a horizontal cross-sectional view of the bonefixation body.
 15. The method of claim 14, wherein the bone fixationbody has one of a polygonal and noncircular closed shape in a horizontalcross-sectional view of the bone fixation body and is bonded to the neckbody after being formed separately from the neck body.
 16. The method ofclaim 14, wherein the bone fixation body includes a location having oneof a polygonal shape and an oval shape in a horizontal cross-sectionalview of the bone fixation body, and the porous metal structure extendsthrough a center of the one of the polygonal shape and the oval shape inthe horizontal cross-sectional view of the location.
 17. The method ofclaim 14, wherein the bone fixation body is not a porous coating but isfabricated separately from the neck body and subsequently engaged to theneck body.
 18. The method of claim 14, wherein the protrusion includes apolygonal shape in the horizontal cross-sectional view.
 19. The methodof claim 14, wherein a distal end surface of the neck body has atrapezoidal shape, a proximal end of the bone fixation body has thetrapezoidal shape, and the solid metal of the trapezoidal shape of theneck body interfaces with the porous metal structure of the trapezoidalshape of the bone fixation body at an interface.
 20. The method of claim14, wherein the protrusion includes a cylindrical shape in a horizontalcross-sectional view.